Ok so here is my problem. Engine was running good with timing at 30* but I adv it 2* in search of the extra bit of power (arc adjustable flywheel) and the bike did not run good. I set timing back to 30 and now the engine blows flames and dies when you hit the throttle hard. I have gone thru the carb completely, float checked all good, reset timing from scratch (tdc, pointer, etc), no change so I did a leak down and found a big leak out of the exh valve. Is it a coincidence that it crapped out after the timing change or could the change somehow cause a leak or a problem? I pulled the head and lapped the valve. Now waiting on a gasket. How do you guys check for a good seal after lapping the valves prior to installation?